A valve device is known in the art, according to which a valve unit is reciprocated in a valve housing by a rotational torque outputted from an electric motor in order to open or close a fluid flow passage. In one of prior arts, a valve device includes a stepping motor, a ball screw member and a female screw member. In the valve device, the ball screw member is rotated by the rotational torque outputted from the stepping motor, wherein the ball screw member is screwed into the female screw member.